Electronic circuits which are suitable for the measurement of mass are known in the art.
FIG. 1 illustrates a first arrangement of a micro scales known in the art which is described in the document “High-Q Longitudinal Block Resonators with Annexed Platform for Mass Sensing Application”, by Zhili Hao and Farrokh Ayazi, GTRC No. 3244, 2006 (U.S. Patent Application Publication No. 20070089519). There is disclosed a piezo-electric structure being hanged on two supporting elements or anchors 11 and 12 which also includes two terminals, respectively a drive terminal and a sense terminal. The drive terminal receives an alternating voltage which causes the structure to oscillate. The arrangement further includes two plates, respectively 13 and 14, which can serve as supports for a mass to be measured. The whole arrangement is the equivalent of one resonance circuit, of the type Bulk Acoustic Wave (BAW) operating in a width mode and not in a thickness mode. The effect of the presence of microparticles on plates 13 and 14 causes the resonance frequency to move and such move can be measured by the electronic circuit forming part of one integrated circuit, thanks to the sensing of the current on the sense terminal.
FIG. 2 illustrates a second device which is known in the art and which is described in U.S. Patent Application Publication No. 2004140296 filed on Aug. 5, 2004, entitled: “Material Sensing Sensor and module using thin film bulk accoustic resonator” by Park Jae Yeong, Lee Heon Min, LG ELECTRONICS INC, also based on a BAW type resonator arrangement (Bulk Acoustic Wave) comprising a reference unit associated to a sensing unit receiving the microparticles to measure. Again, the measurement is based on the detection of a change in the resonance frequency and such change allows the calculation of the mass of the microparticles being measured.
All those devices substantially use metal based materials and, consequently, are not suitable for the measurement of masses of biological material which might interfere with metallic material.